1. Field of the Invention
The present invention relates to a combination of two or more powder coatings of which each color is different, a powder coating composition comprising two or more powder coatings of which each color is different, a coating method using two or more powder coatings of which each color is different, a coating film or a coated substrate prepared by applying to a substrate two or more powder coatings according to the combination of powder coatings, and a coating film or a coated substrate prepared according to the coating method.
2. Discussion of the Related Art
Conventionally, powder coatings have been prepared by adding numerous color pigments to resins, curing agents, additives, mixing the above components, melt-kneading the mixture, followed by cooling, pulverization, and classification. Therefore, in these powder coatings, the powder coatings have to be prepared for each color needed, so that an enormous number of powder coating products are needed.
By contrast, in order to simplify the toning process, there has been proposed a powder coating prepared by forming a composite of several kinds of colored powders.
However, when the powder coatings of which each color is different are uniformly mixed upon use, in cases where of using the mixed powder coatings with particle sizes exceeding 20 .mu.m, the particles of the powder coatings of each color can be generally distinguished by gross examination, thereby making it impossible to obtain a coating film having a homogeneous hue.
On the other hand, as disclosed in Japanese Unexamined Patent No. 4-504431, a method of forming a coating film of a desired hue comprising mixing two or more color powders each having an average particle size of 20 .mu.m or less has been proposed. However, the yield tends to be lowered by down-sizing the particle size to 20 .mu.m or less, and the particles are likely to be agglomerated when they are in the order of 20 .mu.m or less, so that the free flowability of the powder coatings becomes poor, thereby giving rise to such problems as lack of handleability.
Also, a method of improving free flowability by granulating powder coatings by adding a granulating agent solution has been proposed. However, such processes require a large number of production steps, undesirably leading to an increase in costs.
One object of the present invention is to provide a combination of two or more powder coatings of which each color is different, to thereby give a coating film having a homogeneous hue.
Another object of the present invention is to provide a powder coating composition comprising two or more powder coatings of which each color is different, to thereby give a coating film having a homogeneous hue.
Another object of the present invention is to provide a coating method using two or more powder coatings of which each color is different, to thereby give a coating film having a homogeneous hue.
Another object of the present invention is to provide a coating film or a coated substrate having a homogeneous hue prepared by applying to a substrate two or more powder coatings, of which each color is different, according to the combination of powder coatings.
Another object of the present invention is to provide a coating film or a coated substrate having a homogeneous hue prepared by applying to a substrate two or more powder coatings, of which each color is different, according to the coating method described above.
These and other objects of the present invention will be apparent from the following description.